Multi-component coating composition comprising an anhydride containing polymer, a glycidyl component and a phosphonium catalyst

ABSTRACT

A coating composition useful for a finish for automobiles and trucks in which the film forming binder contains reactive binder components of about 
     (a) 25-90% by weight, based on the weight of the binder, of an acrylic polymer having at least two reactive anhydride groups composed of polymerized monomers of an ethylenically unsaturated anhydride and polymerized monomers from the group consisting of alkyl methacrylate, alkyl acrylate and any mixtures thereof, wherein the alkyl groups have 1-8 carbon atoms and the polymer has a weight average molecular weight of about 2,000-50,000; 
     (b) 5-50% by weight, based on the weight of the binder, of a glycidyl component having at least two reactive glycidyl groups; and 
     (c) 0.1-7% by weight, based on the weight of the binder, of a phosphonium catalyst or a blend of a phosphonium catalyst and a tertiary amine catalyst which may or may not contain hydroxyl groups.

This invention is related to a multi-component coating composition.

There are a wide variety of multi-component coating compositionsavailable for finishing substrates. Typically with these compositions,the components are mixed together before application and then theresulting composition is applied by conventional techniques such asspraying and the composition is cured at ambient temperatures or can becured at elevated temperatures. These compositions are used to finishoriginal equipment, automobiles and trucks, refinish automobiles andtrucks, paint structures such as bridges and buildings, paintappliances, metal cabinets and the like.

Representative of such compositions are shown in the following patents:

Gorden et al. U.S. Pat. No. 4,507,411, issued Mar. 26, 1985 shows a twocomponent composition of a functionalized polymeric component andglycidyl component that in the presence of an amine, alcohol, ketimine,acetal or oxazolidine cures at ambient temperatures. However, thecompositions disclosed are not useful for finishes for automobiles andtrucks.

European Patent Application 0,123,793 shows a two component compositionin which one component has an anhydride ring that is opened with anamine and has a second component that contains glycidyl groups. Finishesformed from such compositions are not useful for automobiles and truckssince the finishes whiten and blister on exposure to high humidityconditions and exhibit recoat lifting when repaired within several daysafter the finish has been applied.

British patent 994,881 assigned to Rohm & Haas discloses coatingcompositions comprising polyepoxides, maleic anhydride and the catalystis a quaternary ammonium salt of fluoroboric acid or an amine. Outinventive coating composition does not use quaternary ammonium salts offluoroboric acid. Our inventive coating composition used phosphoniumcatalysts which impart excellent environmental chemical resistance.

U.S. Pat. No. 3,136,736 issued June 9, 1964, to Wyncote et al andassigned to Rohm & Haas discloses a coating composition comprisingpolyepoxides, maleic anhydrides and uses amines or quaternary ammoniumsalts as catalysts. The disclosure does not teach or suggest the use ofphosphonium salts as a catalyst in order to achieve marked improvementin chemical resistance to strong acids and strong bases. Such acomposition is necessary to produce environmentally resistant coatingsin today's atmospheric conditions (e.g., acid rain). In addition, thedisclosed composition has a much higher organic solvent content, highermolecular weight resins and a lower level of anhydride in the resin.

U.S. Pat. No. 4,732,791 issued Mar. 22, 1988, to Blackburn et alconcerns a coating composition comprising polyepoxides, a monomericanhydride curing agent, a low number average molecular weight hydroxylgroup containing polyfunctional function material and amine or opiumsalts. However, the composition disclosed contains monomeric anhydridesrather than polymeric anhydries and contains hydroxyl group containingpolyfunctional material which is not necessary in our composition.

There is a need for a coating composition that provides a high qualityfinish that is useful on an exterior finish for automobiles and trucksthat has excellent adhesion to the substrate to which it is applied,good outdoor weatherability, humidity resistance, excellent appearanceand excellent environmental chemical resistance.

Furthermore, because of environmental concerns about volatile organiccomponents (VOC's) there is a need for such a coating composition with ahigh solids content which retains its sprayability. Many previousmulti-component coating compositions have had to have a solids contentof less than 35 percent to ensure sprayability. There is a need for asprayable coating composition with a solids content of greater than 55percent which retains an excellent mix of other desirable coatingcomposition qualities such as pot life, hardness, durability, humidityresistance and chemical resistance.

SUMMARY OF THE INVENTION

A coating composition containing 20-80% by weight of reactive bindercomponents and 80-20% by weight of an organic carrier: the bindercontains

(a) an anhydride acrylic polymer having at least two anhydride groupsand having a weight average molecular weight of about 2,000-50,000;

(b) a component having at least two reactive glycidyl groups;

(c) a phosphonium catalyst or a blend of a phosphonium catalyst and atertiary amine catalyst which may or may not contain hydroxyl groups.

DETAILED DESCRIPTION OF THE INVENTION

The film forming binder of the coating composition of this inventioncontains components that are mixed together before application. The filmforming binder content of the composition is about 20-80% by weight ofan organic carrier which usually is a solvent for the binder.

The composition forms an excellent clear coating over colored pigmentedfinishes. The coating has good adhesion to the pigmented finish, hasexcellent humidity resistance, excellent environmental chemicalresistance, and is weatherable and durable. The composition is usefulfor finishing the exterior of automobiles and trucks and the compositioncan be pigmented to form a colored finish. Also, the composition can beused over plastic substrates used in automobiled and trucks such asfiller panels, side panels, fender extensions, moldings and other trimparts.

The composition also can be pigmented to form a colored finish. Thesepigmented compositions are useful as exterior original equipmentcoatings for automobiles and trucks and as industrial coatings forappliances, metal cabinets, shelves and the like.

Preferably, the coating composition has a high solids content andcontains about 40-80% by weight binder and 20-60% by weight of organicsolvent. The binder of the composition contains about 25-90% by weightof anhydride acrylic polymer containing at least two anhydride groups,5-50% by weight of a glycidyl containing component and 0.1-7% by weightof a catalyst which is phosphonium or a blend of phosphonium andtertiary amine which may or may not contain hydroxyl groups.

The anhydride acrylic polymer has a weight average molecular weight ofabout 2,000-50,000 determined by gel permeation chromatography usingpolymethyl methacrylate as a standard and preferably, has a weightaverage molecular weight of 3,000-25,000.

The anhydride acrylic polymer is prepared by conventional techniques inwhich the monomers, solvent, and conventional catalysts such as t-butylperbenzoate are charged into a polymerization vessel and heated to about75°-200° C. for about 0.5-6 hours to form the polymer.

The anhydride acrylic polymer is formed by polymerizing monomers ofalkyl methacrylates, or alkyl acrylates or mixtures thereof, where thealkyl groups have 1-12 carton atoms and ethylenically unsaturatedanhydrides (or ethylenically unsaturated dicarboxylic acids which areconverted to the acid anhydride during the polymerization). Optionally,the anhydride acrylic polymer can contain other components such asstyrene, α-methyl styrene, acrylonitrile, methacrylonitrile in amountsof about 0.1-50% by weight.

Typical alkyl acrylates and methacrylates that can be used to form theanhydride acrylic polymer are as follows: methyl methacrylate, ethylmethacrylate, propyl methacrylate, butyl methacrylate, pentylmethacrylate, hexyl methacrylate, octyl methacrylate decyl methacrylate,lauryl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate,butyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate, laurylacrylate and the like. Other components that can be used to form theanhydride acrylic polymer are acrylamide, methacrylamide, acrylo alkoxysilanes such as gamma methacryloyl propyl trimethoxy silane. Also theanhydride acrylic polymer can contain about 0.1-5% by weight of anethylenically unsaturated acid such as acrylic acid, methacrylic acid,itaconic acid, maleic acid and the like.

Typically useful ethylenically unsaturated anhydrides are as follows:itaconic anhydride, maleic anhydride, isobutenyl succinic anhydride andthe like. It is also possible to impart the anhydride functionality tothe anhydride acrylic polymer by using the appropriate ethylenicallyunsaturated dicarboxylic acid which converts to the corresponding acidanhydride by simple heating. Ethylenically unsaturated dicarboxylicacids that can be used are itaconic acid, maleic acid, isobutenylsuccinic acid and the like.

Preferred anhydride acrylic polymers are as follows: styrene/butylmethacrylate/butyl acrylate/ itaconic anhydride, methylmethacrylate/butyl acrylate/itaconic anhydride, butylacrylate/styrene/maleic anhydride/maleic acid, methyl methacrylate/butylacrylate/itaconic anhydride.

The glycidyl component contains at least two glycidyl groups and can bean oligomer or a polymer. Typical glycidyl components are as follows:sorbitol polyglycidyl ether, mannitol polyglycidyl ether,pentaerythritol polyglycidol ether, glycerol polyglycidyl ether, lowmolecular weight epoxy resins such as epoxy resins of epichlorohydrinand bisphenol A., di- and polyglycidyl esters of acids, polyglycidylethers of isocyanurates, such as "Denecol" EX301 from Nagase. Sorbitolpolyglycidyl ether, such as Araldite XYGY-358® from Ciba-Geigy, and di-and polyglycidyl esters of acids, such as Araldite CY-184® fromCiba-Geigy, are preferred since they form high quality finishes.

Glycidyl methacrylate or acrylate containing acrylic polymers can beused such as random and block polymers of glycidyl methacrylate/butylmethacrylate. The block polymers can be prepared by anionicpolymerization or by group transfer polymerization.

The composition contains about 0.1-7% by weight of the binder of acatalyst which is a phosphonium catalyst or a blend of a phosphoniumcatalyst and a tertiary amine which may or may not contain hydroxylgroups. The phosphonium catalyst imparts substantially superior chemicalresistance to the anhydride/epoxy coating compositions of our inventionwhen compared to other known catalysts. It is surprisingly resistant tochemicals such as sulfuric acid, formic acid, sodium hydroxide and saltssuch as calcium sulfate. Examples of the phosphonium catalysts arebenzyl triphenyl phosphonium chloride; ethyl triphenyl phosphoniumbromide; tetra butyl phosphonium chloride; tetra butyl phosphoniumbromide; benzyl triphenyl phosphonium iodide; benzyl triphenylphosphonium bromide; ethyl triphenyl phosphonium iodide and the like.

The composition may also contain a blend of tertiary amine catalystsalong with the phosphonium catalyst. The tertiary amine is added to giveenhanced rheology control. Examples of the tertiary amine catalysts areas follows: triethylene diamine, quinuclidine, dialkyl alkanol aminessuch as dimethyl ethanolamine, diethyl ethanol amine, dibutyl ethanolamine, diethyl hexanol amine and the like, lithium tertiary butoxide,tri(dimethylaminomethyl)phenol, bis(dimethylamino)propan-2-ol, N,N,N¹,N¹ -tetramethylethylenediamine, N,methyldiethanolamine,N,N-dimethyl-1,3-propanediamine and 1-dimethylamino-2-propanol andmulti-hydroxyl amines such as methyl diethanol amine and triethanolamine.

Typical solvents used to prepare the anhydride acrylic polymer and usedas a diluent for the coating composition are as follows: toluene,xylene, butyl acetate, ethyl benzene, higher boiling aromatichydrocarbons, amyl acetate, ethyl acetate, propyl acetate, ethylene orpropylene glycol mono alkyl ether acetates.

In addition to the solvents listed above certain alcoholic solvents arealso useful. The alcoholic solvents under certain use conditions convertportions of the anhydride to a half ester also useful as reactants inthis system. Examples of such alcohols are propanol, isobutanol,methanol, isopropanol tertiary butanol, n-butanol, propylene glycolmonoethyl ether, ethylene glycol mono butyl ether, and other alcoholicsolvents.

The coating composition may also contain components such as monomericanhydrides; acid functional monomeric, oligomeric or polymericcomponents which may or may not contain hydroxyl functionality; hydroxyfunctional polymers; and self-stabilized dispersed resins. Examples ofmonomeric anhydrides are methyl hexahydrophthalic anhydride,hexahydrophthalic anhydride, succinic anhydride and the like. Examplesof such acid functional components are glycolic acid andacrylate/methacrylic acid copolymer and the like. Examples of hydroxylfunctional polymers are polymers such as acrylic polyols, polyesterpolyols, polyether polyols, polyesterurethane polyols and acrylourethanepolyols.

Generally, the composition is applied by conventional techniques such asspraying and electrostatic spraying. The resulting coating can be driedand cured at elevated temperatures of 60° to 200° C. Coatings areapplied to form a finish about 0.5-5 mils thick, and preferably 1-2 milsthick. The finish has excellent gloss, good adhesion to substrate,excellent weatherability, high solids, and excellent environmentalchemical resistance.

To improve weatherability of the clear finish of the coatingcomposition, about 0.1-5%, by weight, based on the weight of the binder,of an ultraviolet light stabilizer or a combination of ultraviolet lightstabilizers can be added. These stabilizers include ultraviolet lightabsorbers, screeners, quenchers and specific hindered amine lightstabilizers. Also, about 0.1-5% by weight, based on the weight of thebinder, of an antioxidant can be added.

Typical ultraviolet light stabilizers that are useful are as follows:

Benzophenones such as hydroxydodecyclobenzophenone, pheonone,2,4-dihydroxybenzophenone, hydroxy-benzophenones containing sulfonicacid groups, 2,4-dihydroxy-3',5'-di-t-butylbenzophenone,2,2',4'-trihydroxybenzophenone esters of dicarboxylic acids,2-hydroxy-4-acryloxyethoxybenzophenone, aliphatic mono-esters of2,2',4-trihydroxy-4'-alkoxybenzophenone,2-hydroxy-4-methoxy-2'-carboxybenzophenone;

Triazoles such as 2-phenyl-4-(2'-4'-dihydroxybenzoyl)triazoles,substituted benzotriazoles such as hydroxyphenyltriazoles such as2-(2'hydroxy-5'-methylphenyl) benzotriazole,2-(2'hydroxyphenyl)benzo-triazole,2-(2'-hydroxy-5'-octylphenyl)naphthotriazole;

Triazines such as 3,5-dialkyl-4-hydroxyphenyl derivatives of triazine,sulfur-containing derivatives of dialkyl-4-hydroxyphenyltriazines,hydroxyphenyl-1,3,5-triazines and such triazines containing sulfonicacid groups, aryl-1,3,5-triazines, orthohydroxyaryl-s-triazine;

Benzoates such as dibenzoate of diphenylolpropane, t-butyl benzoate ofdiphenylolpropane, nonyl phenyl benzoate, octyl phenyl benzoate,resorcinol dibenzoate.

Other ultraviolet light stabilizers that can be used include lower alkylthiomethylene-containing phenols, substituted benzenes such as1,3-bis(2'-hydroxybenzoyl)benzene, metal derivatives of3,5,-di-t-butyl-4-hydroxyphenylpropionic acid, asymmetrical oxalic aciddiarylamides, alkylhydroxyphenylthioalkanoic acid esters,dialkylhydroxyphenylalkanoic acid esters of di- and tri-pentaerythritol,phenyl- and naphthlenesubstituted oxalic acid diamides,methyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,α,α'-bis(2-hydroxy-phenyl)diisopropylbenzene,3,5'-dibromo-2'-hydroxy-acetophenone, ester derivatives of4,4-bis(4'-hydroxy-phenyl)pentaonic acid wherein there is at least oneunsubstituted position ortho to the aromatic hydroxyl groups,organophosphorus sulfides such asbis(diphenyl-phosphinothioyl)monosulfide andbis(diphenyl-phosphinothioyl)disulfide,4-benzoyl-6-(dialkylhydroxybenzyl)resorcinol,bis(3-hydroxy-4-benzoylphenoxy)diphenylsilane,bis(3-hydroxy-4-benzoylphenoxy)dialkylsilane, 1,8-naphthalimides,α-cyano-β,β-diphenylacrylic acid derivatives,bis(2-benzoxazolyl)alkanes, bis(2-napthoxazolyl)alkanes, methylenemalonitriles containing aryl and heteroacyclic substitutes,alkylenebis(dithio)carbamate, 4-benzoyl-3-hydroxyphenoxyethyl acrylate,4-benzoyl-3-hydroxyphenoxyethyl methacrylate, aryl or alkyl-substitutedacrylonitriles, 3-methyl-5-isopropylphenyl-6-hydroxycourmarone,8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazasprio(4,5)decanol-2,4-dione.

Particularly useful ultraviolet light stabilizers that can be used arehindered amines of piperidyl derivatives such as those disclosed inMurayama et al., U.S. Pat. No. 4,061,616, issued Dec. 6, 1977, column 2,line 65, through column 4, line 2, and nickel compounds such as[1-phenyl-3-methyl-4-decanoylopyrazolate(5)]-Ni,bis[phenyldithiocarbamato]-Ni(II), and others listed in the abovepatent, column 8, line 44 through line 55.

The following blend of ultraviolet light stabilizers can be used:2-[2'-hydroxy-3',5'-1(1-1-dimethyl-propyl)phenyl]-benzotrizole andbis-[4-(1,2,2,6,6-pentamethylpiperidyl)]2-butyl-2-[(3,5-t-butyl-4-hydroxyphenyl)methyl] propanedioate. Thestabilizers can be sued in any ratio however, a 1:1 ratio ofbenzotriazole to propanedioate is preferred.

Another useful blend of ultraviolet light stabilizers is2-(benzotriazole-2-VL)-4,6-bis(methylethyl-1-phenyl ethyl)phenol, and2(3 hydroxy-3,5'-ditert amyl phenyl) benzotriazole.

Generally, when the coating composition of this invention is used as aclear coating, it is applied by conventional spraying techniques, to acolor or base coat of an automobile or truck, preferably, electrostaticspraying is used. The coatings are baked at about 60° to 140° C. forabout 10 to 40 minutes. The resulting clear coat or finish is about 1-5mils thick, preferably 1-2 mils thick, and has excellent gloss, goodadhesion to the color coat and excellent weatherability and excellentenvironmental chemical resistance.

The composition can be pigmented to form a colored finish or primer.About 0.1-200% by weight, based on the weight of the binder, ofconventional pigments can be added using conventional techniques inwhich a mill base containing pigment, dispersant and solvent is firstformed. The mill base is then mixed with the composition to form acolored composition. This composition can be applied and cured as shownabove.

The following examples illustrate the invention. All parts andpercentages are on a weight basis unless indicated otherwise. Molecularweights are determined by gel permeation chromatography using polymethylmethacrylate as the standard.

EXAMPLE 1 Anhydride Acrylic Polymer

Styrene/butyl methacrylate/butyl acrylate/itaconic acid(anhydride)copolymer was prepared as follows:

A reactant was loaded with 696.7 parts of xylene and 58.1 parts butylacetate and heated to reflux temperature under nitrogen. The reactor wasfitted with a variable takeoff distillation head to facilitate removalof distillate or reflux as needed.

Then a mixture of the following was added at a uniform linear rate overthree hours while maintaining reflux.

    ______________________________________                                        Styrene monomer        276.1 parts                                            Butyl methacrylate monomer                                                                           844.0 parts                                            Xylene                 28.8 parts                                             Concurrently the following solid monomer was added in                         uniform shots every five minutes                                              Itaconic acid          481.0 parts                                            Also concurrently, but for a period of 200 minutes, the                       following initiator solution was added at a uniform                           linear rate                                                                   Tertiary butyl peroxyacetate                                                                         76.8 parts                                             PM acetate             30.5 parts                                             Xylene                 19.3 parts                                             Total                  1756.5 parts                                           ______________________________________                                    

During the polymerization, water is formed by dehydration of thepolymerized itaconic acid so the anhydride is formed. This water iscontinuously removed by the water separator distillation apparatus untila total of 63.3 parts of water is separated from the distillate.

This polymer solution had a Gardner-Holdt viscosity of Z1+1/2 and ameasured solids of 69.7%. The anhydride content was determined to be0.91. Meq/gm and the acid content to be 0.19 Meq/gm. The molecularweight was measured by gel permeation chromatography to be Mn=2074 andMw=5093.

Acid Polymer

A butyl acrylate/ methacrylic acid copolymer was prepared as follows:

    ______________________________________                                        Propyleneglycol monomethylether-                                                                      1604.0 parts                                          acetate (PM acetate)                                                          Butyl acetate           441.0 parts                                           Xylene                  1243.0 parts                                          This mixture was heated with agitation under nitrogen                         to reflux. Then the following mixture was added at a                          uniform, linear rate over three hours while maintaining                       reflux.                                                                       Butyl acrylate monomer  2427.0 parts                                          Methacrylic acid monomer                                                                              1630.0 parts                                          Tertiary butyl peroxyacetate                                                                          224.0 parts                                           Then the followng mixture was added over ten minutes                          while maintaining reflux temperature                                          Xylene                  200.0 parts                                           Tertiary butyl peroxyacetate                                                                          19.0 parts                                            The reaction mixture was maintained for one hour at                           reflux temperature and then diluted with the following                        PM Acetate              692.0 parts                                           Total                   8480.0 parts                                          ______________________________________                                    

This polymer had a Gardner-Holdt viscosity of Z1+1/2 and a measuredsolids of 52.3%. The acid content was determined to be 2.28 Meq/gm andmolecular weight by gel permeation chromatography was Mn=2762, Mw=6108.

A coating composition using a phosphonium catalyst was prepared bythoroughly blending the following constituents:

    ______________________________________                                                              Parts by Weight                                         ______________________________________                                        Anhydride acrylic polymer (as                                                                         435.2                                                 prepared above)                                                               PM acetate              38.2                                                  Methyl Hexahydrophthalic anhydride                                                                    57.5                                                  Resiflow S ® (acrylic flow additive)                                                              3.4                                                   Butyl acetate           118.7                                                 Araldite CY-184 ® (Epoxy resin from                                                               238.1                                                 Ciba-Geigy)                                                                   Acid polymer (as prepared above)                                                                      174.3                                                 Butanol                 38.8                                                  Tinuvin 292 ® (Ciba-Geigy hindered                                                                13.2                                                  amine light stabilizer)                                                       Tinuvin 1130 ® (Ciba-Geigy UV screener)                                                           20.1                                                  25% Benzyl triphenyl phosphonium                                                                      66.9                                                  chloride in propanol                                                          Total                   1204.4                                                ______________________________________                                    

The resulting coating composition was reduced to a spray viscosity of 35seconds measured with a No. 2 Zahn cup accomplished by adding butylacetate.

The coating composition was sprayed onto a primed metal panel coatedwith a waterborne basecoat and cured at 180°-200° F. and provided aclear coat with excellent color durability, humidity resistance,chemical resistance, and other film properties. The coating compositionwas also sprayed over solvent borne melamine cured basecoat and cured at240°-285° F. The durability, humidity resistance, chemical resistance,and other film properties.

A second coating composition (identical to the one above, except thatamine catalysts were used rather than the phosphonium catalyst) wasprepared by thoroughly mixing together the following components:

    ______________________________________                                                              Parts by Weight                                         ______________________________________                                        Acrylic polymer (as prepared above)                                                                   435.2                                                 PM acetate              38.2                                                  Acetic acid             11.0                                                  Methyl hexahydrophthalic anhydride                                                                    57.5                                                  Resiflow s ® (acrylic flow additive)                                                              3.4                                                   Butyl acetate           118.7                                                 Araldite CY-184 ®   238.1                                                 Acid polymer (as prepared above)                                                                      174.3                                                 Butanol                 38.8                                                  Tinuvin 292 ®       13.2                                                  Tinuvin 1130 ®      20.1                                                  15% bis 2-dimethyl amino ethyl ether                                                                  22.9                                                  in propanol                                                                   20% methyl diethanol amine in propanol                                                                105.2                                                 Total                   1273.6                                                ______________________________________                                    

The resulting coating composition was reduced to a spray viscosity of 35seconds measured with a No. 2 Zahn cup accomplished by adding butylacetate.

The coating composition was sprayed onto a primed metal panel coatedwith a waterborne basecoat and cured at 180°-200° F. and provided aclear coat with excellent color durability, humidity resistance, andother film properties. The coating composition was also sprayed oversolvent borne melamine cured basecoat and cured at 240°-285° F. Theresulting coating exhibited excellent color, durability, humidityresistance, and other film properties. However, the second coatingcomposition (without the phosphonium catalyst) did not exhibit nearlythe chemical resistance as the same composition with the phosphoniumcatalyst. This is illustrated in the test below.

Both coating compositions were sprayed over a primed metal panel coatedwith a solvent borne base melamine crosslinked basecoat and cured atbetween 250° and 265° F.

The following chemical resistance tests were then run:

    ______________________________________                                                         First      Second                                                             Coating with                                                                             Coating with                                                       Phosphonium                                                                              Amine                                             Test             Catalyst   Catalyst                                          ______________________________________                                        10% H.sub.2 SO.sub.4 (24 hours,                                                                10         10                                                uncovered)                                                                    Ford #24 Organic Acid.sup.1                                                                     9         3                                                 (30 minutes, uncovered)                                                       5% NaOH (24 hours,                                                                             10         0                                                 uncovered)                                                                    where 10 = best, 0 = worst                                                    ______________________________________                                         .sup.1 Formic acid, tannic acid, honey and egg albumin mixture           

EXAMPLE 2

A coating composition with the phosphonium and amine catalyst wasprepared by thoroughly blending the following components:

    ______________________________________                                                              Parts by Weight                                         ______________________________________                                        Anhydride acrylic polymer (as                                                                         435.2                                                 prepared in Example 1)                                                        PM acetate              38.2                                                  Butyl acetate           118.7                                                 Methyl hexahydrophthalic anhydride                                                                    57.5                                                  Resiflow S ®        3.4                                                   Acetic acid             4.0                                                   Araldite CY-184 ®   238.1                                                 Acid polymer (as prepared in Example 1)                                                               174.3                                                 Butanol                 38.8                                                  Tinuvin 292 ®       13.4                                                  Tinuvin 1130 ®      20.1                                                  25% Benzyl triphenylphosphoniumchloride                                                               66.9                                                  in propanol                                                                   20% Methyl diethanol amine in propanol                                                                40.2                                                  Total                   1248.8                                                ______________________________________                                    

This clearcoat can be used over waterborne and baked at 200° F. or oversolvent borne and baked at 250°-265° F. (see Example 1 for details).This clear coat offered excellent color, durability, humidityresistance, chemical resistance, sag resistance and other filmproperties over both basecoats. The phosphonium catalyst gives theexcellent chemical resistance and the tertiary amine gives the excellentrheology control.

We claim:
 1. A coating composition comprising 20-80% by weight ofreactive binder components and 80-20% by weight of an organic liquidcarrier; wherein the binder consists essentially of about(a) 25-90% byweight, based on the weight of the binder, of an anhydride acrylicpolymer having at least two reactive anhydride groups that consists ofpolymerized monomers of an ethylenically unsaturated anhydride or anethylenically unsaturated dicarboxylic acid and polymerized monomersselected from the group consisting of alkyl methacrylate, alkyl acrylateand any mixtures thereof, wherein the alkyl groups have 1-8 carbon atomsand the polymer has a weight average molecular weight of about2,000-50,000; (b) 5-50% by weight, based on the weight of the binder, ofa glycidyl component having at least two reactive glycidyl groups; and(c) about 0.1-7% by weight, based on the weight of the binder, of acatalyst which is a phosphonium catalyst or a blend of phosphoniumcatalyst and tertiary amine which may or may not contain hydroxylgroups.
 2. The coating composition of claim 1 in which the glycidylcomponent is selected from the group consisting of polyglycidyl ethersof low molecular weight polyols, epoxy resins of epichlorohydrin andbisphenol A, polyglycidyl esters of polyacids, polyglycidyl ethers ofisocyanurates, glycidyl methacrylate or glycidyl acrylate containingacrylic methacrylate or glycidyl acrylate containing acrylic polymers ora compatible mixture of any of the above.
 3. The coating composition ofclaim 1 in which the anhydride acrylic polymer contains about 0.1-50% byweight of monomers selected from the group consisting of styrene,acrylonitrile, methacrylonitrile and any mixtures thereof.
 4. Thecoating composition of claim 1 in which the anhydride acrylic polymerhas a glass transition temperature of 0° to 75° C. and a weight averagemolecular weight of about 3,000-25,000.
 5. The coating composition ofclaim 3 in which the anhydride acrylic polymer consists essentially or20-40% by weight, based on the weight of the acrylic polymer, of methylmethacrylate, styrene or mixture of methyl methacrylate and styrene,35-55% by weight of an alkyl methacrylate or an alkyl acrylate having2-4 carbon atoms in the alkyl group and 5-55% by weight of polymerizableethylenically unsaturated anhydride or ethylenically unsaturateddicarboxylic acid.
 6. The coating composition of claim 1 in which thecatalyst is benzyl triphenyl phosphonium chloride.
 7. The coatingcomposition of claim 1 in which the catalyst is a phosphonium catalystblended with bis 2-dimethylamino ethyl ether.
 8. The coating compositionof claim 1 in which the catalyst is a phosphonium catalyst blended withmethyl diethanol amine blocked by acetic acid.
 9. The coatingcomposition of claim 5 in which the glycidyl component comprises apolyglycidyl ether of a polyol or a di- or polyglycidylester of an acid.10. The coating composition of claim 9 in which the anhydride acrylicpolymer consists of polymerized monomers of methyl methacrylate, butylacrylate and itaconic acid.
 11. The coating composition of claim 9 inwhich the anhydride acrylic polymer consists of polymerized monomers ofmethyl methacrylate butyl acrylate, styrene, maleic anhydride and maleicacid.
 12. The coating composition of claim 5 in which the anhydrideacrylic polymer consists essentially of polymerized monomers of methylmethacrylate, styrene, butyl acrylate and itaconic acid; andthe glycidylcomponent consists essentially of sorbitol polyglycidyl ether or the di-or polyglycidylester of an acid or a mixture thereof and the catalyst isa phosphonium catalyst.
 13. The coating composition of claim 5 in whichthe anhydride acrylic polymer consists essentially of polymerizedmonomers of methyl methacrylate butyl acrylate, styrene, maleicanhydride and maleic acid;the glycidyl component consists essentially ofsorbitol polyglycidyl ether or the di- or polyglycidylester of an acidor a mixture thereof and the catalyst is a phosphonium catalyst.
 14. Thecoating composition of claim 1 containing about 0.1-200% by weight,based on the weight of the binder, of pigment.
 15. The coatingcomposition of claim 1 in which the acrylic polymer additionallycontains up to about 40% by weight of polymerized monomers selected fromthe group consisting of alkyl acrylate, alkyl methacrylate or mixturesthereof having 9-12 carbon atoms in the alkyl groups.